Section 10.1 Intermolecular Forces

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Section 10.1 Intermolecular Forces
DHfus 6.02 kJ/mol DHvap 40.7 kJ/mol
Answer Now

• Based on the enthalpy values and what you know
  of solids, liquids, and gases, which two states
  of matter are most similar? Which is most unique?

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Liquids and Solids

• Chapter 10

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Types of Intermolecular Forces

• Dipole-Dipole
• Molecules must have dipole
• Opposites attract
• Attractions weaken as distance between dipoles
  increase.
• Hydrogen Bonding
• Type of Dipole-Dipole
• Between H and any highly EN atom. (ie F, N, O)
• Extremely strong attraction

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Types of Intermolecular Forces, 2

• London Dispersion Forces
• Noble Gases and Non-Polar Molecules
• Temporary Dipoles form
• Sometimes called Induced Dipole Forces
• Weaker than Dipole-Dipole
• In molecules with large atoms, dispersion forces
  are often more important than dipole forces.

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Properties and Intermolecular Forces

• What properties do intermolecular forces affect?
• Boiling Point
• Freezing Point
• Vapor Pressure
• Surface Tension
• Capillary Action
• Viscosity

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Practice Problems

• Identify the most important types of
  intermolecular forces present in each of the
  following substances

• In each of the following group of substances,
  pick the one what has the given property and
  justify your answer

• Highest boiling point
• HCl, Ar, or F2
• Highest freezing point
• H2O, NaCl, or HF
• Lowest Boiling Point
• CH4, CH3CH3, or CH3CH2CH3

• Ar
• HCl
• CH4
• CO
• NaNO3

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Vapor Pressure

• Vapor Pressure of a liquid occurs when some
  particles are vaporized just above the surface of
  the liquid.
• Volatile liquids have higher vapor pressures
• REMEMBER
• Patmosphere Pvaporization PHgColumn
• The heat of vaporization (DHvap) is the amount of
  heat required to change 1 mole of liquid to gas.
• Endothermic values

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Vapor Pressure Relationships
Vapor Pressure
Molar Mass
Vapor Pressure
Temperature
Intermolecular Forces
Vapor Pressure
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Vapor Pressure Calculations

• lnPvap -(DHvap/R)(1/T)
• Use 8.314 J/Kmol for R.

The vapor pressure of water at 25oC is 23.8 torr
and the DHvap of water is always 43.9 kJ/mol.
Calculate the vapor pressure of water at 50oC.
Try Me Problem
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Heating Curve

• When a solid is heated, it will absorb energy
  (increase temp) until it begins to melt.

• At melting point and at boiling point, the two
  states of matter are present.
• No change in temperature occurs until all
  particles are converted.

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Phase Diagrams

• Relate the temperature, pressure, and state of
  matter for a substance.
• Triple Point is the point at which all three
  states of matter are present.
• Critical Point is the last temperature and
  pressure combination at which it is possible to
  condense particles to a liquid.

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Phase Diagram of Water
Melting
Evaporation
Sublimation
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What IS Boiling Point?

• Myth

• Fact

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Special Cases

• Superheated liquid A liquid that is heated so
  rapidly that it is actually at a temperature that
  is above the boiling point, but has not
  evaporated.
• Supercooled liquid A liquid that is cooled so
  rapidly that it is actually at a temperature that
  is below the freezing point, but has not
  solidified.

UNSTABLE !
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Section 10.3 Structures and Types of Solids

• Ionic solids
• Molecular solids
• Atomic solids
• All types of solids form crystal lattices.
• The smallest repeatable unit inside a crystal
  lattice is a unit cell.

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Unit Cells

• Simple cubic one atom at each vertex. Polonium
  metal

Basic format
Binary Compound
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Unit Cells, 2

• Body centered cubic at each vertex and in the
  center. Uranium metal

Binary Compound
Basic Format
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Unit Cells, 3

• Face centered cubic at each vertex and in the
  center of each face. Also called Cubic Closest
  Packing structure because each new layer of atoms
  nests into the holes from the layer below.

Basic Format
Binary Compound
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Unit Cells, 4

• Hexagonal Close Packed each atom in the second
  layer lays in a dimple between the atoms in the
  sandwiching layers.

Binary Compound
Basic Format
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Section 10.5 Atomic Solids

• Carbon as diamond
• Physical Properties
• Structure
• Bonding

• Carbon as graphite
• Physical Properties
• Structure
• Bonding

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Section 10.6 Molecular Solids

• Covalent bond length within molecule is shorter
  than the distance between attracted molecules.
• Low melting points, relatively weak IMFs
• Examples of molecules that form Molecular Solids
• Water
• Carbon Dioxide
• Any other covalently bonded molecule

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Section 10.7 Ionic Solids

• The large ions define the shape of the crystal
  lattice. Smaller ions fit in the holes between
  the larger ions.
• Stable
• High Melting Point
• Strong Intermolecular Forces (because ions have
  good dipole moments!)
• Examples of things that form ionic solids
• NaCl
• CsCl
• Any other ionic compoud